Re: [PATCHv2 2/2] i2c: stm32f7: do not set the STOP condition on error

[Alain Volmat <alain.volmat@foss.st.com>]

Hi,

I confirm that a fix is necessary regarding this setting of the stop
condition.  As a matter of fact, the controller is already sending
the stop condition in case of NACK so there is no need to send the
stop condition.
However, this fix is not enough since the nack could be detected
few lines above 

	if (status & (STM32_I2C_ISR_NACKF | STM32_I2C_ISR_ERRORS))
		break;

and in this case the current check would not catch it.

I propose to set the STOP condition upon handling of the transfer
complete.

I've put this fix within a small 3 patches series that I'm going to
send, could you check it to confirm this fixes the issue ?

Regards,
Alain

On Thu, Aug 25, 2022 at 03:36:36PM +0200, Patrice CHOTARD wrote:
> +Alain (with the correct email address ;-))
> 
> Alain, can you have a look a this patch and give your feedback on it.
> 
> On my side i tested it on stm32mp157c-ev1 and stm32mp157c-dk2, i didn't see any regression
> but i prefer to get expert feedback 
> 
> Thanks
> Patrice
> 
> On 8/15/22 16:52, Jorge Ramirez-Ortiz wrote:
> > Sending the stop condition without waiting for transfer complete
> > has been found to lock the bus (BUSY) when NACKF is raised.
> > 
> > Tested accessing the NXP SE05X I2C device.
> > https://www.nxp.com/docs/en/application-note/AN12399.pdf
> > 
> > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
> > ---
> >  drivers/i2c/stm32f7_i2c.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/i2c/stm32f7_i2c.c b/drivers/i2c/stm32f7_i2c.c
> > index 3a727e68ac..14827e5cec 100644
> > --- a/drivers/i2c/stm32f7_i2c.c
> > +++ b/drivers/i2c/stm32f7_i2c.c
> > @@ -485,9 +485,11 @@ static int stm32_i2c_message_xfer(struct stm32_i2c_priv *i2c_priv,
> >  		}
> >  	}
> >  
> > -	/* End of transfer, send stop condition */
> > -	mask = STM32_I2C_CR2_STOP;
> > -	setbits_le32(&regs->cr2, mask);
> > +	if (!ret) {
> > +		/* End of transfer, send stop condition */
> > +		mask = STM32_I2C_CR2_STOP;
> > +		setbits_le32(&regs->cr2, mask);
> > +	}
> >  
> >  	return stm32_i2c_check_end_of_message(i2c_priv);
> >  }